The present invention relates to precision location of aircraft, and has particular relation to such location when the aircraft is on or near a runway.
When an aircraft is far from a runway, it is unnecessary to know exactly (to within 30 cm.) where it is. It is necessary only to know that it is appropriately separated from other aircraft and from the ground. This separation may be on the order of several kilometers. However, such precise information is vital when taxiing, taking off, or (especially) landing, and information as to azimuth and elevation position relative to the runway approach path is most vital. This information is initially provided during aircraft approach to major hub airports by several overlapping ground based radars which are large, powerful, and precisely pointed. Primary guidance during the final approach is from the localizer (VHF frequency) and glide slope (UHF frequency) signals from the airport, which are subject to errors caused by local terrain and obstructions and often can't provide the required accuracy. The microwave landing system (MLS) is planned to be implemented to provide accurate guidance at all major airports, but this solution is uneconomical at smaller facilities.